The present disclosure relates to a fixing device for applying an image fixing process to a sheet and an image forming apparatus provided with the same.
Conventionally, in an image forming apparatus for forming an image on a sheet, a toner image is formed on a photoconductive drum and transferred to the sheet in a transfer unit. The image forming apparatus further includes a fixing unit and the sheet having the toner image transferred thereto is discharged after a fixing process is applied in the fixing unit.
In the fixing unit, the sheet is passed through a fixing nip portion formed between a fixing roller and a pressure roller, whereby the fixing process is applied to the sheet. Conventionally, a fixing unit is known which includes a fixing roller which is inserted into a fixing sleeve and whose diameter increases with an increase in the temperature of the fixing sleeve and a pressure roller which is held in contact with the outer circumferential surface of the fixing sleeve and sandwiches the fixing sleeve between the pressure roller and the fixing roller. The fixing sleeve is loosely fitted on the fixing roller at an ordinary temperature, whereas the fixing sleeve is closely fitted on the fixing roller when the fixing sleeve reaches a fixing temperature.
In the above technology, when the pressure roller is nipped by the fixing roller when the fixing roller is heated, an elastic layer of the fixing roller is largely compressed. Thus, a drive torque for rotating the fixing roller or the pressure roller becomes higher.
The present disclosure was developed in view of the above problem and aims to provide a fixing device capable of suppressing an increase in a drive torque for rotating a roller and an image forming apparatus provided with the same.